The purposes of this project are to find optimal methods of assessing physical activity energy expenditure (PAEE) in a free-living condition and to use these methods to determine the impacts of physical activity frequency, duration, and intensity on health. We previously collected data, using a variety of accelerometers, heart rate monitors, and pedometers, with which we proposed to estimate PAEE in a cohort of healthy young adults. We simultaneously collected laboratory, nutrition, and anthropometric data from the same cohort. We have worked with the listed collaborators to develop and refine methods to analyze the data collected. We have also used the data derived from this study to develop methods for assessing time spent in sedentary behaviors. We have submitted for scientific review a protocol in which we will pilot test several activity monitors in pregnant women with or at risk for diabetes to determine the feasibility of assessing activity patterns and levels of participation in a lifestyle intervention targeting this population. The purpose of this application is to inform development of a subsequent interventional trial to clarify the activity patterns, if any, that are most protective of both mother and fetus against the pregnancy complications attributed to obesity and diabetes. One member of our lab staff (JP) has analyzed data from Sweden and England regarding pregnant and non-pregnant women's activity patterns with an external collaborator (PWF). They found output from wrist-worn accelerometers explained at least 19% of variation in physical activity energy expenditure in non-pregnant women. In a separate cohort, combined accelerometer--heart-rate-monitors, doubly labeled water, and indirect calorimetry were used to describe differences in activity subcomponents and energy expenditure between pregnant and non-pregnant women.